<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="app">hello</div>
  <script>
    let data = {
      msg:"2",
      count:12
    }
   let vm = new Proxy(data,{
      get(target,key){
        console.log('get:',key)
       return target[key]
      },
      set(target,key,newValue){
        console.log('set:',key,newValue)
        if( target[key] === newValue){
          return
        }
        target[key] = newValue
        document.querySelector("#app").textContent = target[key]
      }
    })
    vm.msg = "word"
    console.log(vm.msg)
  </script>
</body>
</html>